Project Summary/Abstract G protein-coupled receptors (GPCRs) play critical roles in physiology, pathophysiology, and organismal development and they are the target of a large fraction of clinically used drugs. Understanding factors that modulate signaling through GPCRs is critical to the full knowledge of signal transduction mechanisms and how they can go wrong in disease. Furthermore, such modulatory mechanisms represent interesting potential drug targets. In the present proposal, we continue to explore the role of Regulators of G protein Signaling (RGS proteins) in physiology, development, and pathophysiology to understand basic signaling mechanisms and to assess the potential of RGS-targeted drugs in the treatment of important medical conditions. This work focuses on two novel mouse models in which RGS-mediated control of the Gi/o signaling pathways is lost. These RGS- insensitive (GaG184S) knock-in models result in enhanced Gai2 and Gao signaling and the mice exhibit an array of interesting phenotypes. Aims 1 & 2 assess the role of RGS proteins and Gai2 signaling in the heart. The RGSi Gai2 mice show protection against ischemia-reperfusion injury but also show worsened heart failure in catecholamine-induced and genetic heart failure models. The aims examine the differential contribution of Gai2 signaling in myocytes and fibroblasts in these two processes and address the mechanisms and specific RGS proteins involved. Aim 3 studies the relative contributions of Gao and Gai2 in GABA function and seizure susceptibility. Aim 4 examines functions of the enigmatic Gao protein. The GaoG184S mice in which Gao signaling is enhanced, show neonatal lethality in homozygotes - virtually none survive past 24 hours - and heterozygotes show a strain-dependent adult lethality at about 15-25 weeks of age. This aim will use genetic methods to understand the unexpected adult lethality. This should provide novel insights into sudden death syndromes as well as uncovering novel potential Gao effector signaling mechanisms.